Spatial Variability of Soil Characterization in Arid Regions Irrigated with Treated Wastewater: Comparative Assessment of Long-Term Impacts on Two Commercial Farms

Soil salinity and alkalinity are major constraints to agricultural productivity in arid regions, particularly where treated wastewater (TWW) is used for irrigation. This study evaluated the spatial variability of water and soil physicochemical properties along Wadi Hanifa, Saudi Arabia, and compared soils from two farms irrigated with TWW for approximately 5 and 15 years to assess the effects of irrigation duration on soil properties. Soil samples were collected from 25 locations along the Wadi using a handheld Global Positioning System (GPS), and water and soil properties were analyzed using standard laboratory procedures. The treated wastewater exhibited moderate electrical conductivity (EC = 2.0 dS m −1 ) and low sodicity hazard (SAR = 1.55), indicating its suitability for irrigation under appropriate management practices. Soils were predominantly coarse-textured and showed considerable spatial variability in salinity and chemical composition. Soil pH remained relatively stable (7.33–8.07), while EC ranged from 0.88 to 2.64 dS m −1 , indicating non-saline to moderately saline conditions across the study area. Comparison of soil profiles from the two farms revealed greater salinity in subsurface layers, particularly at the farm irrigated with TWW for 15 years, where EC reached 4.15 dS m −1 and Na + concentrations reached 16.4 meq L −1 . These observations suggest salt redistribution and accumulation within deeper soil horizons under prolonged irrigation. Overall, soil and water quality in Wadi Hanifa are strongly influenced by spatial variability, coarse soil texture, and arid climatic conditions. The findings highlight the importance of regular monitoring of salinity and sodicity indicators, together with adequate leaching and drainage practices, to ensure the sustainable use of treated wastewater for agricultural production in arid environments.